The present invention relates to imaging apparatus and methods and more particularly relates to an imaging apparatus capable of suppressing inadvertent ejection of a satellite ink droplet therefrom and method of assembling same.
An imaging apparatus, such as an ink jet printer, produces images on a receiver medium by ejecting ink droplets onto the receiver medium in an image-wise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the ability of the printer to print on plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
One such ink jet printer is disclosed in commonly assigned U.S. patent application Ser. No. 09/036,012, titled "Printer Apparatus Capable Of Varying Direction Of An Ink Droplet To Be Ejected Therefrom And Method Therefor" filed Mar. 6, 1998 in the name of Xin Wen. The ink jet printer of the Wen disclosure includes a piezoelectric print head capable of varying direction of an ink droplet to be ejected from the print head. A pair of sidewalls belonging to the print head define an ink channel therebetween containing ink. The print head includes addressable electrodes attached to the side walls for actuating (i.e., moving) the sidewalls, so that the ink droplet is ejected from the ink channel. In this regard, a pulse generator applies time and amplitude varying electrical pulses to the addressable electrodes for actuating the sidewalls.
More specifically, when the side walls of the Wen device inwardly move due to the actuation thereof, a pressure wave is established in the ink contained in the channel. As intended, this pressure wave squeezes a portion of the ink in the form of the ink droplet out the channel. However, as the pressure wave ejects the ink droplet, the pressure wave impacts the sidewalls defining the channel and is reflected therefrom. The pressure wave reflected from the sidewalls establishes a reflected pressure wave in the channel, this reflected pressure wave being defined herein as a "reflected portion" of the incident pressure wave. Of course, if the time between actuations of the sidewalls is sufficiently long, the reflected portion dies-out before each successive actuation of the sidewalls.
However, the reflected portion of the pressure wave may be of amplitude sufficient to inadvertently eject an unintended so-called "satellite droplet" that follows ejection of the intended ink droplet but that occurs before the reflected portion dies-out. Satellite ink droplet formation is undesirable because such inadvertent satellite ink droplet formation interferes with precise ejection of ink droplets from the ink channels, which leads to ink droplet placement errors. These ink droplet placement errors in turn produce image artifacts such as banding, reduced image sharpness, extraneous ink spots, ink coalescence and color bleeding. Thus, a problem in the art is satellite ink droplet formation leading to ink droplet placement errors.
In addition, as stated hereinabove, if the time between actuations of the sidewalls is sufficiently long, the reflected portion of the pressure wave eventually dies-out. Thus, printer speed is selected such that electrical pulses are applied to the addressable electrodes at intervals after each reflected portion dies-out. Such delayed printer operation is required in order to avoid the unintended reflected portion interfering with the intended pressure wave. Otherwise allowing the reflected portion to interfere with the intended pressure wave may result in the aforementioned ink droplet placement errors. However, operating the printer in this manner reduces printing speed because ejection of ink droplets must await the cessation of the reflected portion of the pressure wave. Therefore, quite apart from the aforementioned problem of satellite droplet formation, another problem in the art is reduced printer speed due to presence of the reflected portion of the intended pressure wave.
Therefore, there has been a long-felt need to provide an imaging apparatus capable of suppressing inadvertent ejection of a satellite ink droplet therefrom while maintaining printing speed, and method of assembling the apparatus.